Every solid has its own characteristic electronic energy band structure. This variation in band structure is responsible for the wide range of electrical properties observed in various materials. In semiconductors and insulators, electrons are confined to a number of bands of energy. The term “band gap” refers to the energy difference between the top of the valence band and the bottom of the conduction band. Electrons are able to jump from one band to another, but no electron states can exist within the band gap However, in order for an electron to jump from a valence band to a conduction band, it requires a specific minimum amount of energy for the transition.
Band gap engineering is the process of controlling or altering the band gap of a material. What is needed are improved methods for controlling or altering band gaps in materials.